Found in Radio Electronics from the 90s, this circuit uses a thermistor as a sensor that can have a resistance at room temperature between 10 and 50k. R3 can have values between 10 and 100 k, depending on the thermistor.

Found in Radio Electronics from the 90s, this circuit uses a thermistor as a sensor that can have a resistance at room temperature between 10 and 50k. R3 can have values between 10 and 100 k, depending on the thermistor.